Various polymeric coatings and articles are produced in processes involving use of organic solvents. Such processes require a latent catalyst or latent reaction promoter which can be activated in a controlled fashion. There is an intense effort by environmentalists, researchers, law makers, and industry to promote high solids and 100% solids formulations and processes to reduce or eliminate use of such solvents and attendant costs and environmental contamination.
Various patents, e.g., U.S. Pat. Nos. 4,150,170 (Lazear); 4,181,752 (Martens); 4,330,590 (Vesley); 4,379,201 (Heilmann); and 4,391,687 (Vesley) disclose pressure-sensitive adhesives made via ultraviolet irradiation of a composition consisting of free-radically polymerizable monomers and a free-radical photoinitiator. These patents do not disclose the use of more than one type of photopolymerizable monomer system, cationic organometallic photoinitiators, multiple wavelength irradiation or the use of epoxies in photopolymerizable pressure-sensitive adhesive compositions.
Radiation dual-curable compositions containing unsaturated monomers and epoxy monomers have been described in U.S. Pat. Nos. 4,156,035 (Tsao et al.), 4,227,978, (Barton), 4,428,807 (Lee et al.), 4,623,676 (Kistner), 4,657,779 (Gaske) and 4,694,029 (Land). These compositions include onium salts combined with organic compounds as the photoinitiators. A pressure-sensitive adhesive composition is not taught, nor the use of organometallic complex salts. Multiwavelength irradiation is neither taught or suggested.
U.S. Pat. No. 4,717,605 (Urban et al.) teaches radiation curable adhesives which are based on the combination of an epoxide system and ionic photoinitiators of the triarylsulfonium complex type and at least one ethylenically unsaturated substance which can be polymerized by free-radicals and at least one free-radical photoinitiator. This patent teaches a hardenable glue, and no pressure-sensitive adhesives are disclosed. Also disclosed is the use of two light exposures. Use of organometallic complex salts is not disclosed.
U.S. Pat. No. 4,707,432 (Gatechair) teaches a free-radically polymerizable composition comprising a free-radically polymerizable material and a photoinitiator system comprising an alpha-cleavage or homolytic bond cleavage photoinitiator and a ferrocenium salt. The reference teaches that addition of epoxy, melamine, or vinyl ether containing prepolymers may allow cationic polymerization to ensue as well. Use of multiple wavelengths for photopolymerization is also disclosed. This reference does not teach adhesive compositions, nor that a pressure-sensitive adhesive having good cohesive strength improved pressure-sensitive adhesive properties may be made from an alkyl acrylate homopolymer and an epoxy, when polymerized in the presence of an organometallic complex cation salt.
WO 8802879 (Woods et al.) teaches a free-radically polymerizable composition comprising a free-radically polymerizable material and a photoinitiator system comprising a free-radical photoinitiator and a ferrocenium salt. The composition may contain one or more cationically polymerizable materials. No detail is provided as to the nature of these cationically polymerizable materials, nor do they teach the use of multiple wavelengths for irradiation. Pressure-sensitive adhesives with superior properties are not disclosed.
U.S. Pat. 4,849,320, (Irving) teaches an imaging system containing a combination of two different photoinitiators used with two different polymerizable monomers in combination with irradiation at two substantially different wavelengths. The monomers can be acrylate or epoxies or other cationically polymerizable monomers and the photoinitiators can include ferrocinium, onium salts or an alpha cleavage or homolyric bond cleavage photoinitiator. No pressure-sensitive adhesives are disclosed.
U.S. Pat. No. 4,752,138 (Tumey et al.) teaches a coated abrasive article prepared by polymerizing a combination of epoxy and acrylate monomers using a combination of photoinitiators which can be a ferrocinium, onium salts or an alpha-cleavage of homolytic bond cleavage photoinitiator. This patent does not disclose pressure-sensitive adhesives with superior properties cured via irradiation by multiple wavelengths.
E.P.O. 335629 (Rohm and Haas) discloses photoresists and printing plates comprising cationically polymerizable materials in combination with free-radically polymerizable materials, and photoinitiators for both materials. A multi-wavelength photopolymerization is also disclosed. No pressure-sensitive adhesives are disclosed.
U.S. Pat. No. 3,661,618 (Brookman et al.) concerns a process wherein a solvent-free coating primarily comprising an acrylic ester monomer, is polymerized to a tacky state by being subjected to a beam of high energy electrons. Use of photoinitiators, multiple wavelengths or epoxies is not disclosed.
E.P.O. 344,910, (Palazzotto et al.) discloses a photopolymerizable composition comprising a polymeric precursor, an optional photosensitizer and a two-component curing agent. The polymeric precursors are selected from ethylenically unsaturated monomers, epoxy and polyurethane monomers and mixtures thereof. The curing agent contains an organometallic salt and an onium salt. The compositions are generically disclosed to be useful as adhesives. No specific adhesive compositions or pressure-sensitive adhesives are disclosed.
E.P.O. 344,911 (DeVoe et al.) discloses a polymerizable composition comprising a polymeric precursor, a curing agent containing an organometallic salt and a solvent. The polymeric precursors are selected from ethylenically-unsaturated monomers alone, and in combination with either polyurethane precursors or epoxy monomers. The compositions are generically disclosed to be useful as adhesives. No specific adhesive compositions or pressure-sensitive adhesives are disclosed.
It is an object of the invention to provide a pressure-sensitive adhesive using a cationically polymerizable monomer in combination with a free-radically polymerizable monomer and a photoinitiator system containing at least one salt of a cationic organometallic complex.
It is a further object to provide an adhesive having good adhesive properties using preferred epoxy monomers in combination with preferred free-radically polymerizable monomers.
It is a further object of the invention to provide a pressure-sensitive adhesive having good adhesive properties using an acrylate homopolymer, i.e., without the necessity of the addition of polar copolymerizable monomers.
It is a further object of the invention to provide multiple photoinitiation processes which provide control over polymerization order, thereby providing increased control over properties of the desired composition.
It is a further object of the invention to provide a multiple, photoinitiation process for making a pressure-sensitive adhesive comprising at least one free-radically polymerized monomer, and one cationically polymerized monomer having superior adhesive properties to an identical adhesive otherwise polymerized.